A properly sealed concrete basin doesn't ask for much, and what it does ask for is mostly restraint. Treated well, the surface develops a soft patina that looks better at year ten than year one. Treated carelessly, the same surface etches and stains.
Daily: rinse after use and wipe dry with a soft cloth. Standing water isn't a problem; standing residue, coffee, wine, toothpaste, is what leaves a mark if it's left overnight.
Avoid anything acidic or abrasive. Citric cleaners, bleach, and scouring pads all attack the sealer, and once the sealer is compromised the concrete beneath will absorb stains. A drop of pH-neutral soap on a sponge handles everything normal use throws at it.
Once a year, give it a light re-coat of food-safe, water-based sealer. Clean the basin, let it dry fully, and wipe on a thin coat with a lint-free cloth. Ten minutes of work that resets the surface for another year.
If a stain does set in, don't reach for something stronger, a light hand-sanding with fine paper and a fresh coat of sealer brings it back. Concrete is repairable in a way few sink materials are. That's the whole point of it.